Machines such as, loaders, excavators, dozers, motor graders, and other types of engine-driven machines include a fan system for cooling an engine and other components associated with the machines. The fan system includes multiple fan motors which moves air across a heat exchanger of the machine in order to cool a coolant which in turn, cools the engine and other components. In some arrangements, a hydraulic pump is connected with each of the fan motors to drive the fan motors, independently. This may increase a cost and design complexity of the fan cooling system. Further, in other arrangements, the fan motors are connected in series and driven by a single hydraulic pump.
Furthermore, a pressure valve is also fluidly coupled with each of the fan motors in order to maintain a pressure within the fan cooling system. However, in such arrangements, a back pressure is created across an upstream fan motor during operation of the fan cooling system. This may cause damage to the pressure valves and may cause inefficient operation of the fan system.
U.S. Published Application Number 2014/0373523 (hereinafter referred to as '523 patent application) discloses a hydraulic fan drive with multiple hydraulic motors in series. The hydraulic fan drive includes two fixed displacement hydraulic motors arranged in series supplied with a pressure medium in an open hydraulic circuit by a fixed displacement pump. The hydraulic fan drive also includes a flow control valve, via which a pressure medium volume flows from a line segment between the two hydraulic motors to a pressure sink. The flow control valve is integrated into a housing of the upstream hydraulic motor.
However, use of a common pressure control valve may have a limit to the amount of allowable back pressure before damaging the valve. In addition, the machine may not have the space claim to have two separate fan systems driven by two separate pumps. Thus, there is a need for an improved system for controlling hydraulic driven fans connected in series.